OBJECTIVES: In elderly hemodialysis patients, protein-energy wasting is associated with poor outcome; however, the association between body mass index (BMI) changes over time, and survival has been seldom studied in this particularly frail population. DESIGN AND METHODS: This prospective study recruited 502 hemodialysis patients aged \textgreater/=75 years from the French cohort ARNOS and followed them from 2005 to 2009. BMI changes over time were modeled by individual linear regression models. Survival analyses used frailty Cox models. RESULTS: The population average age was 80.9 years. Forty-one percent of the patients died during follow-up. A 1 kg/m(2) lower baseline BMI was associated with a 4% increase in the risk of death over the study period (hazard ratio [HR] 1.04, 95% confidence interval [1.01-1.08], P = .02). A 5% BMI loss per year was associated with a 52% increase in the risk of death (HR 1.52, 95% confidence interval [1.32-1.75], P \textless .001). In patients who lost weight (\textgreater5% BMI loss per year), the lower was the baseline BMI, the higher was the HR for death. There was a similar trend in the patients with stable weight (5% BMI loss-5% BMI gain per year). In patients who gained weight, the HR was unexpectedly higher than in those with stable weight. CONCLUSIONS: In elderly hemodialysis patients, the impact of the BMI percent change on survival was stronger than that of the baseline BMI. Patients with stable weight had longer survivals than patients who lost or gained weight. Thus, in this population, BMI changes should be regularly assessed. Further studies should assess the safety of weight gain strategies.